metamorphic
Biotite Schist
Biotite Schist (containing K(Mg,Fe)3AlSi3O10(OH)2)
Hardness: 2.5-4; Color: Dark grey to black with shiny flecks; Luster: Pearly to submetallic; Crystal Structure: Monoclinic; Cleavage: Perfect basal; Specific Gravity: 2.7–3.3
- Hardness
- 2
- Color
- Dark grey to black with shiny flecks
- Luster
- Pearly to submetallic
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Physical properties
Hardness: 2.5-4; Color: Dark grey to black with shiny flecks; Luster: Pearly to submetallic; Crystal Structure: Monoclinic; Cleavage: Perfect basal; Specific Gravity: 2.7–3.3
Formation & geological history
Formed through regional metamorphism of shale or mudstone at intermediate temperatures and pressures during mountain-building events (orogenies).
Uses & applications
Used primarily for geological study and as a landscaping stone. Occasional use in electrical insulation or as a filler in paints and rubbers.
Geological facts
The 'sparkly' appearance is due to the alignment of mica flakes, which reflect light effectively. It is a classic indicator of medium-grade metamorphism.
Field identification & locations
Identify in the field by its distinct foliation (schistosity) and shiny, flaky appearance. Found globally in core mountain ranges like the Appalachians or Himalayas.
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